This report describes investigations on ion transport mechanisms and the functional alterations in these mechanisms that occur with aging. These results summarize investigations on: 1. Efficiency of energy coupling declines with age in cardiac muscle sarcoplasmic reticulum. 2. Diminished Ca2+ transport efficiency in sarcoplasmic reticulum accompanies the removal of a 53 kDa glycoprotein. 3. Calcium-induced Ca2+ release in cardiac sarcoplasmic reticulum is unaltered with age. 4. Polypeptide chain interactions are not essential for active Ca2+ transport in skeletal muscle sarcoplasmic reticulum. 5. Interaction of ATP with a low affinity regulatory site on the SR Ca2+ pump prevents polypeptide chain interactions during the Ca2+ transport cycle. 6. Activation of the Na+/H+ exchanger by internal H+ changes the functional subunit composition of the exchanger. 7. Sodium translocation Dy the Na, K pump involves a fast conformational transition. 8. Yohimbine and related positively charged alkaloids block the selectivity filter of Ca2+-activated K+ channels.